The present invention relates to the field of micro mechanical or micro electro-mechanical devices such as ink jet printers. The present invention will be described herein with reference to Micro Electro Mechanical Inkjet technology. However, it will be appreciated that the invention does have broader applications to other micro mechanical or micro electro-mechanical devices, eg. micro electro-mechanical pumps or micro electro-mechanical movers.
Micro mechanical and micro electro-mechanical devices are becoming increasingly popular and normally involve the creation of devices on the xcexcm (micron) scale utilizing semi-conductor fabrication techniques. For a recent review on micro-mechanical devices, reference is made to the article xe2x80x9cThe Broad Sweep of Integrated Micro Systemsxe2x80x9d by S. Tom Picraux and Paul J. McWhorter published December 1998 in IEEE Spectrum at pages 24 to 33.
One form of micro electro-mechanical devices in popular use are ink jet printing devices in which ink is ejected from an ink ejection nozzle chamber. Many forms of ink jet devices are known.
Many different techniques on ink jet printing and associated devices have been invented. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Recently, a new form of ink jet printing has been developed by the present applicant, which is referred to as Micro Electro Mechanical Inkjet (MEMJET) technology. In one form of the MEMJET technology, ink is ejected from an ink ejection nozzle chamber utilising an electro mechanical actuator connected to a paddle or plunger which moves towards the ejection nozzle of the chamber for ejection of drops of ink from the ejection nozzle chamber.
The present invention concerns improvements to a thermal bend actuator for use in the MEMJET technology or other micro mechanical or micro electro-mechanical devices.
In accordance with a first aspect of the present invention, there is provided a thermal actuator for micro mechanical or micro electro-mechanical devices, the actuator comprising a supporting substrate, an actuator extension portion, a first arm attached at a first end thereof to the substrate and at a second end to the extension portion, the first arm being arranged, in use, to be conductively heatable, a second arm attached at a first end to the supporting substrate and at a second end to the extension portion, the second arm being spaced apart from the first arm, the first arm being arranged, in use, to undergo thermal expansion, thereby causing the actuator to apply a force to the extension portion, and wherein the first arm comprises at least one heat sink element substantially at a point of maximum heating of the first arm, being the point where, in use, maximum heating of the first arm would occur.
It has been found by the applicant that the provision of the heat sink element can improve the operational characteristics of the thermal bend actuator in that the maximum temperature in the first arm can be reduced, and in that a more uniform temperature profile can be achieved throughout the first arm. This can maximise the thermal expansion induced in the first arm.
The heat sink element can be located substantially in the middle of the first arm.
The heat sink element may be arranged to interconnect the first and second arm.
The heat sink element can comprise at least one tab body connected to a main body of the first arm.
The tab body may be connected to the main body via a first thinned neck portion.
The first arm can comprise a conductive layer whereby the first arm is conductively heatable.
The actuator may be arranged in a manner such that a current can be supplied to the conductive layer through the supporting substrate.
The first and second arms are preferably formed from substantially the same material.
The extension portion can comprise a paddle structure. Accordingly, the actuator may be used inside a liquid ejection chamber, the paddle structure being movable for the ejection of liquid from the chamber.
The first conductive arm can be formed from titanium nitride and the second arm can be formed from titanium nitride.